Vacuum cleaners generally remove dirt, dust and other debris from a surface by a combination of a suction force, generated by a motor-driven fan, and some form of mechanical agitation of the floor surface. The mechanical agitation often takes the form of a rotating brush bar which is driven by a motor or by an air turbine. The rotating brush bar ‘beats’ the carpet pile while the suction force ‘sucks’ dirt and dust from the surface.
Agitation of a carpet by a brush bar inevitably causes some damage to the carpet and also causes wear on the brush bar and the drive system for the brush bar.
There have been various proposals for tools which make use of a vibrating airstream to promote the release of dirt from a carpet. U.S. Pat. No. 5,400,466 shows a cleaning head with a loudspeaker supported and sealed within the cleaning head which directs airwaves towards the surface in the frequency range of 10-200 Hz or 200-500 Hz.
However, tools of this kind have a disadvantage in that they can be noisy in use. Also, the use of a loudspeaker near to a source of suction causes problems with operation of the loudspeaker since there is a tendency for the loudspeaker cone to be sucked towards the source of suction.